Introduce Time delay in Mutate Http Filter plugin

I have a requirement where we would be querying clientid's from postgres DB and pass each of clientid to one of HTTP API and dump the output to file output.
Now the DB contains some 100K unique clientid's and i need to pass each clientid to API input by introducing some delay else API will timeout.
Is there any suggestions on this how can we achieve this using logstash ?

If you are concerned that the API cannot handle multiple concurrent requests then limit the number of pipeline.workers. If the API needs time to recover before handling another request then you could use a sleep filter.